System and method for the on-board production of reductants

ABSTRACT

A system is provided for the on-board production of reductants. The system comprises a fuel tank adapted to directly or indirectly supply a first fuel stream and a second fuel stream. An engine is in fluid communication with the fuel tank, and is configured to receive the first fuel stream and create an exhaust stream. The system further includes an emission treatment unit to treat the exhaust stream. A fuel conversion unit is configured to receive the second fuel stream, and also receive a stream comprising oxygen to partially oxidize at least a portion of the second fuel stream thereby forming reductants. In addition, the fuel conversion unit is configured to supply a reductant stream comprising the reductants to the exhaust stream. The invention further provides a method for the on-board production of reductants including supplying a first fuel stream to an engine, wherein the engine is configured to create an exhaust stream. A second fuel stream and a stream comprising oxygen are supplied to a fuel conversion unit. At least a portion of the second fuel stream is partially oxidized in the fuel conversion unit to form reductants, and a reductant stream comprising the reductants is supplied to the exhaust stream. The selective catalytic reduction of NOx present in the exhaust stream is performed.

FIELD OF THE INVENTION

The invention includes embodiments that relate to an emission treatmentsystem, and more particularly to the on-board production and supply ofreductants to an emission treatment system.

BACKGROUND OF THE INVENTION

Current emission control regulations necessitate the reduction ofpollutant species in diesel engine exhaust. NOx, principally NO and NO₂,contributes to smog, ground level ozone formation and acid rain. NO isproduced in large quantities at the high combustion temperaturesassociated with diesel engines. NO₂ is formed principally by the postoxidation of NO in the diesel exhaust stream. Exhaust aftertreatmentdevices achieve NOx reduction by using a reductant agent. The reductantagent is added to the exhaust gas entering the aftertreatment device andreacts with NOx over a catalyst in a process of selective catalyticreduction (SCR). Typical reducing agents may include light hydrocarbonsand oxygen bearing compounds like alcohols.

Known methods of supplying the reductants may involve supplying thereducing agents and the fuel separately or may involve chemicallyproducing the reducing agent in situ from the fuel itself. Such methodstypically employ complex subsystems such as special purpose pumps,filters, storage tanks and the like. Additionally, these systems alsorequire valuable space and specialized materials, thereby involvingadditional expenses. Accordingly, there is need for an improved systemand method for producing and supplying reductants to provide betteroverall economy and ease of operation.

SUMMARY OF THE INVENTION

Embodiments of the invention provide systems and methods for theon-board production and supply of reducing agents for use in hydrocarbonbased SCR treatment. Briefly stated, in accordance with one embodimentof the invention, there is provided a system for the on-board productionof reductants comprising a fuel tank adapted to directly or indirectlysupply a first fuel stream and a second fuel stream; an engine in fluidcommunication with the fuel tank, wherein the engine is configured toreceive the first fuel stream and create an exhaust stream; an emissiontreatment unit to treat the exhaust stream; a fuel conversion unitconfigured to receive the second fuel stream, and also receive a streamcomprising oxygen to partially oxidize at least a portion of the secondfuel stream thereby forming reductants, the fuel conversion unit alsoconfigured to supply a reductant stream comprising the reductants to theexhaust stream.

In accordance with another embodiment of the invention, there isprovided a method for the on-board production of reductants comprisingsupplying a first fuel stream to an engine, wherein the engine isconfigured to create an exhaust stream; supplying a second fuel streamand a stream comprising oxygen to a fuel conversion unit; partiallyoxidizing at least a portion of the second fuel stream in the fuelconversion unit to form reductants; supplying a reductant streamcomprising the reductants to the exhaust stream; and performing aselective catalytic reduction of NOx present in the exhaust stream.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary system for the on-boardproduction of reductants in accordance with an embodiment of theinvention.

FIG. 2 is a schematic diagram of an exemplary system for the on-boardproduction of reductants in accordance with an alternative embodiment ofthe invention.

FIG. 3 is a schematic diagram of an exemplary system for the on-boardproduction of reductants in accordance with an alternative embodiment ofthe invention.

FIG. 4 illustrates a method for the on-board production of reductants inaccordance with an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of an exemplary system 10 for the on-boardproduction of reductants for treating NOx emissions from an engine. Thesystem 10 includes an engine 12 that is directly supplied with a firstfuel stream 14 from a fuel tank 16. An on-board fuel conversion unit 18is directly supplied with a second fuel stream 20 from the fuel tank 16.If desired, the fuel tank 16 may be adapted to indirectly supply thefirst fuel stream 14 to the engine 12 and the second fuel stream 20 tothe fuel conversion unit 18 via a single fuel stream 21 exiting the fueltank that is split, or comprises a slip stream, to form the first andsecond fuel streams, as illustrated in FIG. 2.

Referring to FIGS. 1 and 2, the fuel tank 16 may be adapted to supplythe first fuel stream 14 to a first fuel pump 22, wherein the first fuelpump is adapted to pump the first fuel stream to the engine 12. The fueltank 16 is also adapted to supply the second fuel stream 20 to a secondfuel pump 24. The second fuel pump 24 pumps the second fuel stream 20 tothe fuel conversion unit 18. A portion of the first fuel stream 14 isburnt in the engine 12 during operation of the engine and an emission ofexhaust gases containing NOx is produced thereby. The exhaust gases,thus produced, are discharged through an exhaust stream 30. The exhauststream 30 carries the exhaust gases to an emission treatment unit 32where the exhaust stream is treated by selective catalytic reduction.The resulting treated exhaust steam 38 is exhausted into the atmosphere.

The systems and methods of the invention allow for the use of one fueltank 16 for carrying the fuel instead of requiring an extra storage tankfor an SCR reductant. This is advantageous from an implementation anddistribution point of view. For example, the system can be installed onexisting locomotive engines.

The fuel conversion unit 18 converts at least a portion of the fuelentering the unit via the second fuel stream 20 into reductants. Anoxygen supply stream 39 comprising oxygen is supplied to the fuelconversion unit 18 to partially oxidize the fuel within the unit. Theoxygen supply stream 39 may be comprised of air from the surroundingatmosphere, an exhaust stream from the engine (not shown), or any othersuitable oxygen source.

Any fuel conversion unit 18 known to those having skill in the art maybe used in the system and methods of the invention, wherein the fuelconversion unit is capable of producing reductants effective for theselective catalytic reduction of NOx. In a preferred embodiment, thefuel conversion unit 18 is a catalytic partial oxidation unit. The fuelconversion unit 18 may produce reductants including, but not limited tohydrogen, as well as other hydrocarbon reductants such as diesel fuel,partially cracked diesel fuel, gasoline, olefins, paraffins,isoparaffins, olefinic esters, oxygenates, and aromatics such asnapthalenes and naphtha. Hydrogen has been shown to be advantageous as aco-reductant with hydrocarbons, such as but not limited to oxygenates,alkanes, alkenes, acetylenes, aromatics, and naphthalenes.

Reductant stream 40 exiting the fuel conversion unit 18 supplies thereductants directly to exhaust stream 30, and subsequently to theemission treatment unit 32 wherein the reductants are used to performthe selective catalytic reduction of NOx. If desired, the fuelconversion unit 18 may supply the reductant stream 40 to a reductantpump 50, wherein the reductant pump is adapted to pump at least aportion of the reductant stream to the emission treatment unit 32 viaexhaust stream 30, as shown in FIGS. 1 and 2. In another embodiment ofthe invention (not shown), a portion of the reductant stream 40 may besent back to the fuel tank 16 or to the engine 12 directly. Completeconversion of the fuel in the fuel conversion unit 18, while desired, isnot necessary because most fuels can also be used as reductants inhydrocarbon based SCR.

The first fuel pump 22, second fuel pump 24, and reductant pump 50 mayeach be an electrically actuated fuel pump. In another embodiment of theinvention, the pumps 22, 24 and 50 may be a fuel injector.

Referring to FIG. 3, a condenser 54 may be disposed in fluidcommunication with the fuel conversion unit 18 for condensing at least aportion of the reductant stream 40 exiting the fuel conversion unit. Thetemperature of the condenser 54 is set so that the most activereductants and/or a higher concentration of reductants remain in thegaseous form and are supplied to the exhaust stream 30 and emissiontreatment unit 32 via gaseous reductant stream 58. Most activereductants mean those reductants which are most effective for theselective catalytic reduction of NOx. reduce NOx If desired, thereductant stream 58 may be supplied to pump 50. The condenser 54 alsosupplies a condensed reductant stream 56 which is recycled back to thefuel tank 16

Referring to FIGS. 1 and 2, the amount of reductant that is produced bythe fuel conversion unit can be controlled using a NOx sensor 60 that isplaced down stream of the emission treatment unit 32. The NOx sensor 60measures the concentration of NOx in the treated exhaust steam 38exiting the emission treatment unit 32. The NOx sensor 60 sends a signalrepresenting the NOx concentration in the treated exhaust stream 38 to asecond fuel controller 62. The second fuel controller 62 integrates theprocessed information and determines if the system parameters areindicative of proper control of the treated exhaust stream 38, and mayfurther determine whether there is a need for supply of reductants tothe emission treatment unit 32. Accordingly, the second fuel controller62 regulates the flow of the second fuel stream 20, entering the fuelconversion unit 18, based on the signal received from the NOx sensor 60.The second fuel pump 24 is in communication with the second fuelcontroller 62, and the controller directly controls and monitors theoperation of the second fuel pump to inject a portion of the second fuelstream 20 into the fuel conversion unit 18.

The NOx sensor 60 may alternatively be used to directly control theamount of reductant flow, i.e. the reductant stream 40 flow, into theexhaust stream 30 and emission treatment unit 32, as shown in FIGS. 1-3.The NOx sensor 60 sends a signal representing the NOx concentration inthe treated exhaust stream 38 to a reductant controller 64. Thereductant controller 64 regulates the flow of the reductant stream 40entering the emission treatment unit 32, based on this signal. Thereductant pump 50 is in communication with the reductant controller 64,and the controller 64 directly controls and monitors the operation ofthe reductant pump to inject at least a portion of the reductant stream40 into the emission treatment unit 32 via exhaust stream 30.

Structurally, the controllers 62 and 64, as shown in FIGS. 1-3, may eachbe a conventional microcomputer, including conventional components suchas a microprocessor unit, input/output ports, read-only memory, randomaccess memory, read-out displays, and conventional data bus.Furthermore, the controllers 62 and 64 may each include amicro-controller or a solid-state switch to communicate with the sensor60. In one embodiment, the controllers 62 and 64 may each be anelectronic logic controller that is programmable by a user. In anotherembodiment, each controller 62 and 64 may include an analog-to-digitalconverter accessible through one or more analog input ports.

As will be recognized by those of ordinary skill in the art, thecontrollers 62 and 64 may be embodied in several other ways. In oneembodiment, the controllers 62 and 64 may include a logical processor(not shown), a threshold detection circuitry (not shown) and an alertingsystem (not shown). Typically, the logical processor is a processingunit that performs computing tasks. It may be a software construct madeup using software application programs or operating system resources.

The emission treatment unit 32, in one embodiment of the invention mayinclude after-treatment devices in which NOx in the engine exhauststream 30 is continuously removed by reacting with active reductants inthe presence of a catalyst to produce N₂. In one embodiment of theinvention, the catalysts may include oxidation catalysts that convert aportion of incoming NO to NO₂. In another embodiment of the invention,the catalysts may be lean NOx catalysts capable of reducing NOx in anoxygen rich environment. Efficiency of the reduction catalysts may befurther increased in the presence of additional reductants. Suchadditional reductants may typically include hydrocarbon compounds. Anumber of hydrocarbon reductants may typically be disposed along withthe fuel as an additive component, as described below herein.

The fuel used in the embodiments of the invention include any fuelsuitable for operation of the engine 12, such as gasoline. In oneembodiment of the invention, the fuel may be normal diesel fuel. Inanother embodiment of the invention, the fuel may be a renewable fuel.In one embodiment of the invention, the renewable fuel is green dieselfuel. In a preferred embodiment of the invention, the renewable fuel isbiodiesel, which consists of fatty acid methyl esters and may be madefrom vegetable oil, animal fat, or waste grease. In another embodiment,the biodiesel is used as a blend with conventional diesel.

In yet another embodiment of the invention, Fischer-Tropsch diesel maybe used as a renewable fuel that at times may be produced from biomass.Fischer-Tropsch or gas-to-liquid (GTL) fuels are typically created by aFischer Tropsch process that makes liquid diesel fuel from a syntheticmix of gases including CO and H₂. Typical Fischer-Tropsch fuels maycontain very low sulfur and aromatic content and very high cetanenumbers. Fischer-Tropsch diesel fuels typically reduce regulated exhaustemissions from the engines and the vehicles where this fuel is used.Additionally, the low sulfur content of these fuels may enable use ofadvanced emission control devices.

In yet another embodiment of the invention, an additive component may beblended into the fuel before the fuel is supplied to the engine 12 andfuel conversion unit 18. For example, the additive component may bemixed with the fuel in fuel tank 16. Examples of additive componentsthat may be used in the invention, include but are not limited tooxygenate reductants such as alcohols, aldehydes, ketones, ethers,esters, or combinations thereof. The alcohols may include methanol,ethanol, iso-propanol and the like. In addition, ethanol/diesel,ethanol/biodiesel and ethanol/gasoline fuel blends are readily availableon the market, so no additional infrastructure would be required to mixthe additive component with the fuel if desired. The concentration ofthe additive component in the fuel may typically be in the range ofabout 0.5 percent to about 20 percent by weight of the total fuel.

In one embodiment of the invention, hydrocarbon reductants may be usedin order to aid in the production of oxygenated hydrocarbons, i.e.oxygenate reductants, as represented by equation (1) below.

Hydrocarbons (HC)+O₂=>oxygenated HC   (1)

NOx+oxygenated HC+O₂=>N₂+CO₂+H₂O   (2)

The hydrocarbon reductants may include propene, ethane, diesel fuel,partially cracked diesel fuel, gasoline, or any other suitablehydrocarbons and the oxygenated hydrocarbons may include methanol,ethanol, propanol, butanol, pentanol, hexanol, methanal, ethanal,propanal, butanal, propenal, acetone, 2-butanone, and 3-penten-2-one andany combination thereof. Although the lean-NOx reducing reaction is acomplex process comprising many steps, one of the reaction mechanismsfor lean NOx catalysts may be summarized as follows. Ahydrocarbon-enriched reductant may be converted to an activated,oxygenated hydrocarbon that may interact with the NOx compounds to formorgano-nitrogen containing compounds, which are then reduced to N₂.Through these or other mechanisms the NOx species are eventually reducedto N₂.

The principles of the invention are not limited to any particular typeof engine. One of ordinary skill will recognize that other embodimentsof the invention may be suited for many of the combustion-poweredvehicles. For example, internal combustion engines that are used inrailroad locomotives, in vehicles that run on roads such as trucks,municipal transport vehicles, city buses, cars and other passengervehicles or in ships may be installed with this type of reductant supplysystem. The engine may also be a liquid fueled engine, a compressionignition engine, a gasoline engine, and any combination thereof. Thegasoline engine may include a lean burn gasoline engine. A lean burnengine is one that produces an oxygen rich exhaust, which is defined asan exhaust having a higher molar ratio of oxygen than the total molarratio of reductive compounds such as carbon-monoxide, hydrogen,hydrocarbons, and oxygenated hydrocarbons. Examples of such lean burnengine systems may include diesel engines, some natural gas oralternative fuel engines, liquid or gaseous-fueled turbine engines andvarious lean burn gasoline engine systems.

FIG. 4 illustrates an exemplary method for supplying reductants to anemission treatment unit in accordance with one embodiment of theinvention. As will be appreciated by one of ordinary skill in the art,the method may represent one or more of processing strategies such asevent-driven, interrupt-driven, multi-tasking, multi-threading, and thelike. As such, various steps or functions illustrated herein may beperformed in the sequence illustrated, in parallel, or in some casesomitted. Likewise, the order of processing is not necessarily requiredto achieve the objects, features and advantages of the invention, but isprovided for ease of illustration and description. Although notexplicitly illustrated, one of ordinary skill in the art will recognizethat one or more of the illustrated steps or functions may be repeatedlyperformed depending on the particular strategy being used.

To this end, beginning at block 102, a first fuel stream 14 is suppliedto an engine 12, wherein the engine is configured to create an exhauststream 30. A second fuel stream 20, and an oxygen supply stream 39 aresupplied to a fuel conversion unit 18 as shown in block 104. Referringto block 106, at least a portion of the second fuel stream 20 ispartially oxidized in a fuel conversion unit 18 to form reductants. Areductant stream 40 comprising the reductants is supplied to the exhauststream 30 as shown in block 108. Referring to block 110, the selectivecatalytic reduction of NOx present in the exhaust stream 30 isperformed.

All cited patents, patent applications, and other references areincorporated herein by reference in their entirety.

All ranges disclosed herein are inclusive of the endpoints, and theendpoints are combinable with each other.

It is to be noted that the terms “first,” “second,” and the like as usedherein do not denote any order, quantity, or importance, but rather areused to distinguish one element from another. The modifiers “about” and“approximately” used in connection with a quantity are inclusive of thestated value and have the meaning dictated by the context (e.g., includethe degree of error associated with measurement of the particularquantity). The use of the terms “a” and “an” and “the” and similarreferents in the context of describing the invention (especially in thecontext of the following claims) are to be construed to cover both thesingular and the plural, unless otherwise indicated herein or clearlycontradicted by context.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:

1. A system for the on-board production of reductants comprising: a fueltank adapted to directly or indirectly supply a first fuel stream and asecond fuel stream; an engine in fluid communication with the fuel tank,wherein the engine is configured to receive the first fuel stream andcreate an exhaust stream; an emission treatment unit to treat theexhaust stream; a fuel conversion unit configured to receive the secondfuel stream, and also receive a stream comprising oxygen to partiallyoxidize at least a portion of the second fuel stream thereby formingreductants, the fuel conversion unit also configured to supply areductant stream comprising the reductants to the exhaust stream.
 2. Thesystem of claim 1, further comprising: a first fuel pump adapted to pumpthe first fuel stream from the fuel tank to the engine.
 3. The system ofclaim 1, further comprising: a second fuel controller that receives asignal representing a concentration of NOx in a treated exhaust streamexiting the emission treatment unit, the controller regulates the flowof the second fuel stream into the fuel conversion unit in accordancewith the received signal.
 4. The system of claim 3, further comprising:an NOx sensor located downstream of the emission treatment unit and incommunication with the second fuel controller, the sensor measures theconcentration of NOx in the treated emission stream and sends a signalto the second fuel controller representing the measured concentration.5. The system of claim 3, further comprising: a second fuel pump incommunication with the second fuel controller to pump the second fuelstream to the fuel conversion unit.
 6. The system of claim 1, furthercomprising: a reductant controller that receives a signal representing aconcentration of NOx in a treated exhaust stream exiting the emissiontreatment unit, the reductant controller regulates the flow of thereductant stream into the exhaust stream in accordance with the signal.7. The system of claim 6, further comprising: an NOx sensor locateddownstream of the emission treatment unit and in communication with thereductant controller, the sensor measures the concentration of NOx inthe treated emission stream and sends a signal to the reductantcontroller representing the measured concentration.
 8. The systemaccording to claim 6, further comprising: a reductant pump incommunication with the reductant controller to pump at least a portionof the reductant stream into the exhaust stream.
 9. The system accordingto claim 1, wherein the reductants comprise hydrogen, hydrocarbons, or acombination thereof.
 10. The system according to claim 9, wherein thereductants comprise diesel fuel, partially cracked diesel fuel,gasoline, an olefin, paraffin, isoparaffin, olefinic ester, aromatic,oxygenate reductant, or a combination thereof.
 11. The system accordingto claim 10, wherein the oxygenate reductant comprises an alcohol,aldehyde, or ketone, or a combination thereof.
 12. The system accordingto claim 1, wherein the emission treatment unit is a selective catalyticreduction treatment unit.
 13. The system according to claim 1, whereinthe first and second fuel streams comprise diesel fuel, biodiesel fuel,green diesel fuel or Fischer-Tropsch fuel, or any combination thereof.14. The system according to claim 13, wherein the first and second fuelstreams comprise biodiesel fuel.
 15. The system according to claim 1,wherein the engine is a liquid fueled engine, a compression ignitionengine, or a gasoline engine, or any combination thereof.
 16. The systemaccording to claim 15, wherein the gasoline engine is a lean burngasoline engine.
 17. The system according to claim 1, wherein the firstfuel stream and second fuel stream comprise an additive component. 18.The system according to claim 17, wherein the additive component is analcohol, aldehyde, or ketone, or a combination thereof.
 19. The systemaccording to claim 1, wherein the reductant stream is a gaseousreductant stream, and the method further comprises: a condenserconfigured to receive the gaseous reductant stream exiting the fuelconversion unit and condense at least a portion of the gaseous reductantstream.
 20. The system according to claim 19, wherein the condenser unitis configured to supply the condensed portion of the reductant stream tothe fuel tank, and supply the remaining gaseous reductant stream to theexhaust stream, and wherein the reductants present in the gaseousreductant stream are more active than the reductants present in thecondensed portion of the reductant stream.
 21. A method for the on-boardproduction of reductants comprising: supplying a first fuel stream to anengine, wherein the engine is configured to create an exhaust stream;supplying a second fuel stream and a stream comprising oxygen to a fuelconversion unit; partially oxidizing at least a portion of the secondfuel stream in the fuel conversion unit to form reductants; supplying areductant stream comprising the reductants to the exhaust stream; andperforming a selective catalytic reduction of NOx present in the exhauststream.
 22. The method of claim 21, wherein the first and second fuelstreams are supplied directly or indirectly from a fuel tank.
 23. Themethod of claim 21, further comprising: sensing a concentration of NOxin a treated exhaust stream exiting the emission treatment unit; andregulating the flow of the second fuel stream into the fuel conversionunit in accordance with the sensed signal.
 24. The method of claim 21,further comprising: sensing a concentration of NOx in a treated exhauststream exiting the emission treatment unit; and regulating the flow ofthe reductant stream into the exhaust stream in accordance with thesensed signal.
 25. The method according to claim 21, wherein thereductants comprise hydrogen, hydrocarbons, or a combination thereof.26. The method according to claim 25, wherein the reductants comprisediesel fuel, partially cracked diesel fuel, gasoline, an olefin,paraffin, isoparaffin, olefinic ester, aromatic, oxygenate reductant, ora combination thereof.
 27. The method according to claim 26, wherein theoxygenate reductant comprises an alcohol, aldehyde, or ketone, or acombination thereof.
 28. The method according to claim 21, wherein thefirst and second fuel streams comprise diesel fuel, biodiesel fuel,green diesel fuel, Fischer-Tropsch fuel, and any combination thereof.29. The method according to claim 28, wherein the first and second fuelstreams comprise biodiesel fuel.
 30. The method according to claim 21,wherein the engine is a liquid fueled engine, a compression ignitionengine, a gasoline engine, and any combination thereof.
 31. The methodaccording to claim 21, wherein the first fuel stream and second fuelstream comprise an additive component.
 32. The method according to claim31, wherein the additive component is an alcohol, aldehyde, or ketone,or a combination thereof.
 33. The method according to claim 21, whereinthe first and second fuels streams are supplied by a fuel tank, and themethod further comprises: condensing a portion of the reductants formedby the fuel conversion unit; and supplying the condensed reductants tothe fuel tank.